Preheat your oven to 350°F (175°C) and spray a 13 x 9-inch baking dish with non-stick cooking spray.

Cut gluten-free bread into small pieces and toast on an ungreased baking sheet for 5-10 minutes.

Mix together light brown sugar, pumpkin pie spice, and ground cinnamon, then sprinkle evenly in the baking dish.

Layer the toasted gluten-free bread pieces over the sugar mixture in the baking dish.

In a bowl, whisk together eggs, milk, granulated sugar, vanilla extract, canned pumpkin, and remaining pumpkin pie spice until smooth. Pour over the bread.

Combine gluten-free flour, brown sugar, pumpkin pie spice, salt, and melted butter until coarse crumbs form, then sprinkle over the bread.

Bake for 1 hour until golden brown and a toothpick comes out clean.

Prepare the glaze by whisking powdered sugar, vanilla extract, milk, and maple syrup until smooth.

Drizzle glaze over casserole after cooling for 10-15 minutes, cut into squares, and serve warm.